The present invention relates to a semiconductor device and a method for fabricating the same. More particularly, the present invention relates to a semiconductor device, in which a titanium nitride film having excellent characteristics is formed on the surface of windows, holes or grooves having a width or diameter, depending on the shape of the window, hole or groove opening (in this specification they are called holes having a diameter generically). The present invention is especially directed to providing such film in holes having a large aspect ratio (height of hole/minimum diameter of hole), and a method for fabricating the same.
Recently, with remarkable increase in integration density in semiconductor devices, the diameter of contact holes has become significantly smaller and regions doped with impurity formed in the surface portion of semiconductor substrates have become very much thinner When wiring made of an aluminium or aluminium alloy film is connected with the surface of such a considerably thin region doped with impurity through a contact hole and heat treatment is effected in order to increase the reliability of the devices, aluminium is diffused into the impurity doped region and pierces through the p-n junction, which gives rise to a difficulty that the p-n junction is destroyed.
In order to remove such a difficulty, a method has been proposed, by which reaction between aluminum and the semiconductor substrate is prevented by interposing a barrier layer made of titanium nitride between the wiring made of aluminium or alloy thereof and the surface of the semiconductor substrate.
Since titanium nitride has a relatively low resistivity has excellent in stability at high temperatures and is chemically stable, it is possible to prevent a reaction between the wiring and the semiconductor substrate and to improve the reliability of the semiconductor device by using titanium nitride as a barrier layer.
Heretofore a reactive sputtering method has been most widely used for fabricating a titanium nitride film. Since it is difficult to obtain a high purity titanium nitride target for sputtering the film using pure Argon, a method for fabricating a titanium nitride film, by which a high purity titanium target is used and titanium is made to react with nitrogen in a discharge gas, is usually utilized. The formation of a titanium nitride film by such a reactive sputtering method is disclosed in J. Vac. Sci. Technol., A4(4), 1986, pp 1850-1854.
On the other hand, when the width or the diameter of the holes described above is very small and the aspect ratio (height of hole/minimum diameter of hole) is large, it is considerably difficult to form a titanium nitride film having an appropriate film thickness on the inner surface of such a hole by the reactive sputtering method described above.
That is, when a titanium nitride film is formed by the reactive sputtering method, the thickness of the titanium nitride film is not uniform, and is very small around the bottom portion of the hole, which decreases remarkably performance of the film as a barrier layer. Further, since the thickness of the titanium nitride film thus obtained is not uniform and has a profile, with an overhang when aluminium or an aluminium alloy is deposited thereon to form the wiring, cavities or voids are formed therein, which decreases the reliability of the semiconductor device produced.
As methods for fabricating a titanium nitride, film apart from the reactive sputtering method, there have been proposed an evaporation method (J. Vac. Sci. Technol., 21(1), May/June, 1982, pp. 14-18) and a low pressure CVD method (U.S. Pat. No. 4,570,328, JP-A-61-69969). However, in these literatures, the formation of a titanium nitride film having a uniform thickness on the inner surface of a considerably fine hole having a large aspect ratio, and the property of the titanium nitride layer thus formed as the barrier, are not mentioned; and it is strongly desired to find a method for fabricating a semiconductor device provided with a titanium nitride film, which has a uniform thickness and is excellent in its property as a barrier, on the inner surface of a fine hole having a large aspect ratio in such a semiconductor device.